1. Field of the Invention
The present invention relates to an image processing method and an image processing device for processing images of the optic disc region of a photographed ocular fundus under examination.
2. Description of the Related Art
In the field of methods for diagnosing the ophthalmic disorder of glaucoma, image processing is known which evaluates the shape and size of the optic disc (hereinafter referred to simply as the disc or disc region) in an image of the ocular fundus.
When the magnitude of optic disc cupping is to be evaluated via image analysis, they define the diameter ratio C/D of the diameter of the optic disc cupping, called the “cup”, and the diameter of the optic disc, called the “disc” (see Japanese Patent No. 3594468).
The medial region lying between the disc region and the cup region is termed the “rim” and observation of the width of this rim is one method for the examiner to diagnose glaucoma.
According to Japanese Patent No. 3594468, an image of the ocular fundus containing the disc region is displayed, and the disc region is specified manually in the displayed image using a mouse, keyboard, input stylus or the like. The cup region is then computed automatically from the height thereof.
Japanese Laid-Open Patent Application 2008-73188 also proposes a method of automatically computing the cup line (cup contour) from the degree of bending of the vessels in the ocular fundus image.
Japanese Laid-Open Patent Application 2006-280411 discloses a method in which the disc line (disc contour) and cup line (cup contour) are computed using a spline approach to derive therefrom the C/D ratio, which is compared with the C/D ratio from the measurements with a table of C/D ratios for normal eyes created in advance in order to diagnose ophthalmic disorders.
Document, “Application in Auto-recognition and Pseudo-stereoscopic Image Generation of the Optic Disc Using Images with Blood Vessels Erased for a System of Assisted Diagnosis of Ocular Fundus Images”, IEICE Transactions, D, Vol. J89-D, No. 11, pp. 2491-2501, 2006, also proposes a method of erasing blood vessel regions from a captured ocular fundus image, automatically recognizing the optic disc using the image from which the blood vessel regions are erased, and generating a pseudo-stereoscopic image.